[poj2337]求字典序最小欧拉回路

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
#define N 2020
using namespace std;
string str[1010];
int cnt,in[30],out[30];int ans[1010];
int edgenum=0;
int head[N],vet[N],pri[N],next[N],flag[N],len[N];
void add(int u,int v,int w)
{
    edgenum++;vet[edgenum]=v;next[edgenum]=head[u];head[u]=edgenum;
    pri[edgenum]=w;
}
void dfs(int u)
{
    int e=head[u];
    while(e>0)
    {
        int v=vet[e];
        if(flag[e]==0){
            flag[e]=1;dfs(v);ans[cnt++]=pri[e];
        }
        e=next[e];
    }
}
int main()
{
    int cas,n;scanf("%d",&cas);
    while(cas--)
    {
        scanf("%d",&n);
         for(int i = 0;i < n;i++)
            cin>>str[i];
        sort(str,str+n);//要输出字典序最小的解，先按照字典序排序
        //for(int i=0;i<n;i++)len[i]=strlen(str[i]);
        edgenum=0;memset(head,0,sizeof(head));
        memset(flag,0,sizeof(flag));
        memset(in,0,sizeof(in));memset(out,0,sizeof(out));
        int start=10000;
        for(int i=n-1;i>=0;i--){
            int u=int(str[i][0])-‘a‘,v=int(str[i][str[i].length()-1])-‘a‘;
            add(u,v,i);out[u]++;in[v]++;
            if(u<start)start=u;if(v<start)start=v;
        }
        int cc1=0,cc2=0;
        for(int i=0;i<26;i++){
            if(out[i]-in[i]==1){
               cc1++;start=i;
            }else if(out[i]-in[i]==-1)cc2++;else if(out[i]-in[i]!=0)cc1=3;
        }
        if(!((cc1==0&&cc2==0)||(cc1==1&&cc2==1))){
           printf("***\n");continue;
        }
        cnt=0;dfs(start);
        if(cnt!=n){printf("***\n");continue;}
        for(int i = cnt-1; i >= 0;i--)
        {
            cout<<str[ans[i]];
            if(i > 0)printf(".");
            else printf("\n");
        }
    }
}